1. Field of the Invention
The present invention relates to an iron-based rare-earth nanocomposite magnet and a method for producing such a magnet. The present invention also relates to a rapidly solidified alloy to make an iron-based rare-earth nanocomposite magnet and to a bonded magnet including an iron-based rare-earth nanocomposite magnet powder.
2. Description of the Related Art
A nanocomposite permanent magnet, having a nanocrystalline structure in which a hard magnetic phase such as Nd2Fe14B1 phase (which will be sometimes referred to herein as a “2-14-1 phase”) and soft magnetic phases such as an iron-based boride and α-Fe are magnetically coupled together, is currently under development. In the “2-14-1 phase”, Nd may be replaced with any other rare-earth element, Fe may be partially replaced with Co and/or Ni, and B may also be partially replaced with C (carbon).
The applicant of the present application discovered that when Ti was added to an alloy with a particular composition, the nucleation and growth of the α —Fe phase could be restricted and the crystal growth of the 2-14-1 phase could be advanced preferentially while the molten alloy was being cooled. And the applicant of the present application disclosed a nanocomposite magnet, having a structure in which the 2-14-1 phase is distributed uniformly in the fine iron-based boride and α —Fe phases as a result of the addition of Ti, and a method for producing such a magnet in Patent Document No. 1.
The Ti-containing nanocomposite magnet disclosed in Patent Document No. 1, of which the soft magnetic phases are mostly iron-based borides, has a coercivity of about 500 kA/m to about 1,000 kA/m, which is extremely high for a nanocomposite magnet, but can exhibit a remanence of at most about 0.9 T.
Recently, in the field of electronic products including small-sized motors and sensors, magnets that have a higher remanence than the magnet disclosed in Patent Document No. 1 are in high demand. To increase the remanence, the percentage of the α —Fe phase, having a higher saturation flux density than the 2-14-1 phase or the Fe—B phase, may be increased.
Patent Documents Nos. 2 and 3 disclose rare-earth nanocomposite magnets including α —Fe as their main phase. A nanocomposite magnet of that type would achieve a high remanence exceeding 0.9 T.                Patent Document No. 1: Japanese Patent No. 3264664        Patent Document No. 2: Japanese Patent Application Laid-Open Publication No. 8-162312        Patent Document No. 3: Japanese Patent Application Laid-Open Publication No. 10-53844        
However, the conventional α —Fe based nanocomposite magnets disclosed in Patent Documents Nos. 2 and 3 have such a low coercivity of 400 kA/m or less that it is difficult to actually use such magnets in various products.